High temperature battery cell comprising stress-free hollow fiber bundle

ABSTRACT

Thermal stressing of hollow fibers constituting the electrolyte-separator in a high temperature battery cell, and of certain other elements thereof, is avoided by suspending the assembly comprising the anolyte tank, the tubesheet, the hollow fibers and a cathodic current collector-distributor within the casing and employing a limp connection between the collector-distributor and the cathode terminal of the cell.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 939,156, filed Sept. 1,1978 and now U.S. Pat. No. 4,332,868.

BACKGROUND OF THE INVENTION

High temperature batteries, such as sodium/sulfur batteries, in whichthe electrolyte-separator takes the form of a large number of hollowfibers are now well known. In discharge of such a sodium/sulfur batterycell, the anodic reactant, molten sodium, gives up electrons to anexternal circuit and forms Na⁺ ions which migrate through the fiberwalls to the catholyte. The cathodic reactant, molten sulfur, takes upelectrons from the external circuit to form sulfide anions. Thecatholyte is thus converted to a mixture or solution of sodiumpolysulfide(s) with or in sulfur.

Hollow fiber batteries of this type, and methods of making them, aredescribed in the following U.S. patents, the disclosures of which areincorporated herein by reference for all purposes which such referencesmay serve:

    ______________________________________                                        U.S. PAT. NO.                                                                              Subject Matter                                                   ______________________________________                                        3,476,602    Hollow fiber type high-temperature                                            batteries.                                                       3,672,995    Hollow fiber electrolyte-separator                                            materials.                                                       3,679,480    Hollow fiber type electrical cell                                             assembly.                                                        3,703,412    Sequence of melting anolyte and                                               catholyte.                                                       3,749,603    MoS.sub.2 coated foil as current collect-                                     ing means in Na/S cell.                                          3,765,944    C-coated foil as current collector.                              3,791,868    Method of making a battery cell                                               having a coiled foil as a current                                             collector.                                                       3,829,331    Hollow fibers of sodium borate glass.                            3,917,490    Method of grinding tubesheet glasses.                            4,050,915    Cooling a nascent, melt-spun, hollow                                          glass fiber.                                                     ______________________________________                                    

The prior art cells described in the above-listed patents preferably arehermetically sealed, but do not necessarily have to be closed by sealsor welds requiring high temperatures for their information. In fact,when such a cell is so insulated and heated that its upper end remainsrelatively cool during operation, the openings in the upper casing wallthrough which the leads pass, and/or which function as fill ports, canbe sealed with materials such as pitches, tars or high-melting waxes.However, for the majority of commercial applications contemplated forhigh temperature batteries, it will not be very practicable to maintaindifferent parts of the component cells at different temperatures. Forthis reason, and by reason of obvious safety concerns, a more permanentand reliable method of sealing, as by welding or use of solder glasses,is indicated.

The latter sealing methods are feasible but, in the rigid structures ofthe prior art, have been found to result in thermally induced stresseswhich can damage the tubesheet, the seals themselves and/or some of thefibers, which are relatively fragile. When forming welds or sealsbetween the high melting or refractory materials of construction mostsuitable for high temperature battery cells, it is difficult to achievea high degree of cross-sectional uniformity and to attain even coolingof the seals. Consequently, dimensional changes resulting in shifting ofthe inner assembly (anolyte cup, tubesheet, fibers and foil wraps; seedrawings) within the casing and relative motion within the assemblyitself tend to occur. If either of these movements is hampered, theresultant stresses can crack the seals or the tubesheet and/or breaksome fibers (usually just below the tubesheet).

It is not apparent from the literature (including patents) on thesubject of high temperature batteries, that the preceding problem hasbeen heretofore recognized. Neither has any method of constructing suchbatteries been described which would inherently avoid or remedy theproblem.

OBJECTS OF THE INVENTION

It is a primary objective of the present invention to provide aconfiguration for high temperature battery cells which does not sorestrain expansive/contractive motions, of or within the assemblycomprising the fibers, that the seals, tubesheet or fibers are subjectedto potentially damaging stresses.

A further object is to provide a battery cell which is improved withrespect to the manner in which an inner assembly is disposed orpositioned within the casing.

Another object is to provide a more rugged, hollow fiber type batterycell which is better adapted to commercial applications, such as inbattery-powered vehicles.

A further object is to provide a battery cell in which an inner assemblyis supportingly engaged with a wall of the outer casing and iselectrically connected to the terminals of the casing but motion withinor of the assembly as a result of temperature changes is essentiallyunhampered.

An additional object is to provide a high temperature battery cell whichis improved in that the number of sealing engagements between dissimilarmaterials is reduced.

Another object is to facilitate construction of a hollow fiber typebattery cell in which the weight of the cathodic current collectingmeans is transferred by a (non-conductive section of a) central core ormandrel to the tubesheet and does not stress the fibers.

An additional object is to provide a hollow fiber type battery in whichthe anolyte cup, the tubesheet and a non-conductive core sectionconstitute a unitary body of essentially constant compositionthroughout.

Another object is to provide a method of fabricating hollow fiber typebattery cells which satisfies other structural requirements withoutsubjecting the inner assembly to stresses during or subsequent toformation of such seals as are required.

Yet other objects will be made apparent to those skilled in the art bythe following specifications and claims.

SUMMARY OF THE INVENTION

The appended drawings will now be briefly described.

FIGS. 1-4 are semi-schematics which depict four different embodiments ofthe invention, i.e., four different cells in which the inner assembly isengaged at one end, or around its middle, with a wall of the casing andis connected at one end, or at each end, through a limp link, to anelectric terminal of the cell.

FIG. 1 is a semi-schematic plan view, looking down on a generallycylindrical cell of the invention which has not been charged withcatholyte or anolyte. A vertical cross-section through line A--A of thefigure is depicted in FIG. 1-A. FIG. 1-B depicts an enlarged view of alower right hand part (encircled) of the vertical cross-section in FIG.1-A. The cell of FIG. 1 consists of an external metallic casing fittedwith electrical terminals and an inner assembly consisting of a metallicanolyte reservoir, a non-conductive tubesheet, a central core aroundwhich is disposed a hollow fiber bundle and a cathodic currentcollecting means, the latter being joined to the casing through a limpfoil link and an intervening metallic tape coil. The lower portion ofthe casing is adapted to contain a body of catholyte which will surroundthe fiber bundle and occupy the unfilled spaces between the fibers.

FIGS. 2 and 2-A likewise depict in semi-schematic manner a cell similarto that of FIG. 1 but containing molten sodium (the anolyte) and amolten sodium polysulfide (the catholyte). In this embodiment, the limplink is a soft wad of a conductive fiber immersed in a molten sodiumpolysulfide. The anolyte tank is nonmetallic and supports the tubesheet(and fiber bundle, etc.) through a non-conductive extension of thecentral core. The core section within the tank is hollow, has aperforated wall and contains a separate anodic current distributingmeans. The tubesheet, tank and non-conductive core section constitute aunitary body, the formation of which does not require seals betweendissimilar materials.

FIGS. 3, 3-A and 3-B are semi-schematic and depict an unfilled,column-shaped cell of the invention in which the horizontalcross-section is generally square and of essentially constant size fromtop to bottom of the cell. FIG. 3 is a top view, in plan. FIG. 3A is avertical cross-section taken through line A--A in FIG. 3 and FIG. 3B isa horizontal cross-section (of the entire cell, viewed from above)through line B--B in FIG. 3A. FIG. 3C is a magnified view of a segmentof a "ladder" comprising three spaced apart foil strips ("rails") and analternating sequence of hollow fiber and wire lengths ("rungs") held inplace by thin layers of fugitive cement. The fibers are open at one endand closed at the other end, and a length of spacer tape is disposed asan extra "rail" adjacent to but not touching the closed fiber ends. Thisladder is rolled up on a mandrel (together with a bead of tubesheetpaste) to form the lower half of the inner assembly of the cell. In thisembodiment, the casing consists of an electrically non-conductivematerial, such as a glass or ceramic. The anolyte tank is metallic andhas an upper, tubular section extending through and sealed to thecasing, the tank body acting as the anodic current collector and itsupper end acting as the anode terminal of the cell. The cathodic currentcollector is an array of wire lengths disposed between and generallyparallel to the fiber lengths. The relative positions of the fibers andwires are maintained by the three coiled foil strips within the bundleand by a coil of a relatively thick, soft metal spacer tape below thefibers. The core is square in cross-section, is closed at both ends and,in this particular embodiment, is not engaged with the tubesheet. Acathode terminal post passing through and sealed to the bottom of thecasing is engaged with a metal disc resting on the inner surface of thecasing bottom. A powder of low-melting, otherwise suitable metalparticles is disposed between the metal disc and the spacer tape coil,to act (when melted) as a limp connecting link in operation of the cell.

FIG. 4 is a semi-schematic which depicts--in vertical cross-section--anembodiment of the invention in which the inner assembly is positionedand supported in the casing by contact along an equatorial line, andeach of the connections between the assembly and the anode and cathodeterminals includes a limp (foil) link. The periphery of the tubesheetextends "radially" out of the assembly as a ridge or lip and is(slidingly) engaged with the surface of a conforming groove in thecasing side wall. The casing is glass or ceramic, the anolyte cup ismetallic and the weight of the non-fiber components below the tubesheetis transferred to the tubesheet by a central core which (anon-conductive portion of) is integral with the tubesheet. Aliquid-tight catholyte cup is disposed around the portion of theassembly below the tubesheet.

The cell of FIG. 4 is not depicted in horizontal cross-section or planview, but may have either a circular or square cross-sectional shape (asin FIG. 1 or 3).

DEFINITION OF TERMS

As used herein, the terms listed below are intended to have the meaningsstated:

Hollow Fiber: A capillary fiber having an outer diameter of about 6500microns or less.

Cathodic and Anodic Terminals: The positive and negative poles,respectively, of the cell, when it is discharging.

Limp Link: A member which lacks stiffness; is not self-supporting. Maybe a body of liquid.

Fluid: A liquid, gas, vapor or froth.

Tight Contact: Contact of the type resulting when a flexible tape iswound, under tension, to form a coil.

Foraminous: As applied to the wall of a core section within the anolytetank, a sufficiently open wall structure as to offer no substantialresistance to flow of the anolyte therethrough.

Inert: Not detrimentally reactive to an intolerable extent.

Anolyte: The body of material comprising the electrochemical reactantwhich provides electrons (to an external circuit) during discharge ofthe cell. May be synonymous with a reversibly consumable anode, as inthe case of a molten alkali metal.

Catholyte: The body of material comprising the electrochemical reactantwhich accepts electrons (from an external circuit) when the cell is ondischarge.

THE INVENTION DEFINED

The present invention is a battery cell and the method by which it isfabricated.

More precisely, the cell of the invention may be defined as:

a battery cell in which the electrolyte/separator is in the form of aplurality of hollow fiber lengths and the cell is so constructed thathigh temperatures may be employed in its fabrication or use withoutsubjecting the cell components to thermally induced stresses of suchmagnitude as to damage them,

said cell comprising:

a casing which is fitted with electrical leads adapted to function aspositive and negative terminals of the cell and has top, bottom and sidewalls; and

an inner assembly disposed in the casing and so engaged therewith thatmotion of the assembly therein is limited but motion of the assemblycomponents as a result of thermally induced dimensional changes is nothampered,

said assembly comprising:

(a) an upper member having the general shape of a bell or an invertedcup, the bottom edge of which is sealingly engaged with afluid-impervious, electrically inert, generally disc-like, tubesheethaving opposed, generally horizontal, upper and lower faces, said uppermember and the tubesheet together defining a tank,

(b) a bundle of said fibers, in generally parallel array, spacedlaterally apart, and each having an open end and a closed end andconsisting of a fluid-impermeable, electronically non-conductive, bution conductive, material; said fibers passing generally verticallythrough and being sealingly engaged with said tubesheet body in suchdisposition that their open ends are coincident with or adjacent to saidupper tubesheet face and communicate with said tank, their closed endsdepending from said lower face,

(c) a first current collecting/distributing means disposed in but notfilling the spaces between said fibers and joined by a first connectingmeans to one of said leads,

(d) a second current distributing/collecting means joined to the otherof said leads by a second connecting means and so located that, whensaid tank is substantially filled with a liqid, the latter distributingmeans is in contact with the liquid,

at least one of said first and second connecting means comprising alimp, electrically conductive link,

said casing and upper member being adapted to prevent fluidcommunication between the tank interior and the portion of the casinginterior external to said assembly.

A comparably precise definition of the method of fabricating the cell isdeferred until later herein. However, said method may be summarilycharacterized as comprising such steps, in such sequence, that theexpansive/contractive motions which result when the (anolyte)tank-to-casing and tank-to-tubesheet seals are formed are not sohampered as to detrimentally stress the seals, the tubesheet or thefibers.

It is a further advantage of the invention, both as a cell design and asa fabrication method, that incorporation of additional structuralelements which better adapt high temperature battery cells forcommercial operation is facilitated. That is, the essential concept ofsuspending the inner assembly within the casing and using at least onelimp link between one of the current collecting/distributing means andthe correpsonding terminal(s) makes feasible--for example--theutilization of an extended core as a means of supporting the tubesheetso that it can take the weight of the (cathodic) current collecting andconnecting means off the fibers and at the same time is less likely tosag upon prolonged operation of the cell at elevated temperatures.Similarly, utilization of a buoyant core to support a tubesheet againstsag is facilitated.

The drawings are intended not only to illustrate specific embodiments,but also to exemplify various ways in which the separate cell elementsmay be altered and/or associated, without going outside the bounds ofthe invention.

In hollow fiber type battery cells, the material contained in the fibersmust have a high electrical conductivity, since the current path is atleast as long as the fibers. Thus, since a molten metal is a much betterconductor than a solution in sulfur of the metal polysulfide(s), theanolyte (sodium) will generally be disposed inside the fibers in asodium/sulfur cell of this type. However, the utility of the cells ofthe present invention is not restricted to operation with the anolyteinside and the catholyte outside of the fibers.

In the preceding description of the embodiments depicted in thedrawings, the tank above the tubesheet was designated as an anolyte tankand the liquid in which the fibers would be (or are) immersed isdesignated as the catholyte. The current collecting/distributing meansand cell terminals were corresondingly designated. This terminology isconsistent with prior art disclosures of hollow fiber cells and was usedto simplify the initial discussion of the drawings. However, thesubsequent definition of the invention is not so limited and is directedto cells in which a suitable catholyte may be disposed on either side ofthe fiber wall and the anolyte disposed on the other side.

It should be noted that the term "current" is used herein in theconventional sense, as opposite in direction to electron flow. Whetheror not current is being "distributed" or "collected" from the liquidabove (or below) the tubesheet at any given time during operation of thecell of course depends on whether or not that liquid is the anolyte orcatholyte and whether or not the cell is being discharged or charged.

Cell fabrication--A representative sequence of cell fabrication steps (athrough p) follows. Reference to FIGS. 1, 1-A and 1-B, wherein theindividual cell elements are numbered, will be helpful to following thedescription. See also FIG. 3C.

(a) Hollow glass fibers are melt-spun, essentially as described in theabove cited U.S. Pat. No. 4,050,915. These are used to make long"ladders" in which two or more parallel, spaced-apart, thin, narrow,flexible foil strips (1) are "rails" and cut lengths (2) of fiber, openat one end (3) and sealed shut at the other end (4), and laid at rightangles across the strips, constitute "rungs". The fiber lengths (2) areheld in place on each strip by a thin layer of a thermally-degradeableor "fugitive" cement (not shown) such as ordinary rubber cement thinnedwith methylene chloride, for example. (The relative size (diameter) ofthe fibers is greatly exaggerated in all of the drawings except FIG.1-B.)

A length of electrically conductive sheeting, such as a wide ribbon (5)of aluminum foil, is coated with carbon or MoS₂ as described in theabove cited U.S. Pat. Nos. 3,765,944 or 3,749,603, respectively. Theribbon is wider than a fiber length and has a thickness equal to fromabout 0.1 to 0.2 of the outer diameter of a fiber. It is positioned withrespect to the fiber ladder so that, when they are rolled up together,the open ends of the fibers will extend beyond one lateral edge of thefoil and the portion of the foil adjacent to the other edge will extendbeyond the closed ends of the fibers as a "skirt" (6).

A flexible, conductive spacer tape (7), having a thickness at leastequal to 1.1 fiber diameters, is provided, the width of the tape beingsomewhat less than the width of the foil skirt. This tape will usuallybe longer than the foil, to provide a tape end or tab that can later beused to form a limp connection to the casing bottom.

(b) The fiber ladder, foil and tape are rolled up together around alength of aluminum or stainless steel tubing (a mandrel) which is longerthan the foil is wide and protrudes at one end of the developing roll.the tape is disposed in the roll so that one edge generally coincideswith the skirt edge, thereby ensuring that the closed fiber ends (4) arespaced apart from the other tape edge. The protruding portion of themandrel is not shown. At a later stage in the procedure, the latterportion is cut off and the tubing length then constitutes a central core(8) around which the portion of the assembly below the tubesheet isdisposed.

A bead of paste--a viscous suspension of glass or ceramic particles in afugitive medium (see the above cited U.S. Pat. No. 3,917,490)--isapplied to the fibers, adjacent their open ends, as they enter the nipof the developing roll. The successive spirals of the latter beadlaterally cohere in the completed "jelly roll" to form a self-supportingdisc which will constitute the tubesheet (9), when densified (cured).

The outermost wrap of the foil may be adhered at its end to the nearestunderlying wrap by a thin layer of a suitable cement (such as the abovedescribed rubber cement) to form a sleeve which serves to protect thesubjacent fibers during subsequent handling. The alternating wraps offoil "skirt" and spacer tape form a coil (10) which may be regarded as alaminated metal body, at one end of the roll, which is joined with theportions of the foil wraps between the fibers. (The foil wrapsconstitute a current collecting/distributing means and the laminatedbody--the coil--functions as part of a connecting means.) The core actsto a limited extent as a collector/distributor but its primaryelectrical role is as a supplemental portion of the connecting means.)

(c) The tubesheet-to-be is "green cured" by placing the sub-assemblycomprising it in a sealed container and providing a means of condensingor absorbing the solvent vapors evolved from the cement(s) and thepaste. In this way, the rate of drying is limited and the resultinggreen-cured disc is chalk-like and can be readily machined. Molecularsieves are a convenient means for absorbing the evolved vapors.

(d) If it is necessary to grind the edges of the disc, as to shape orsize it, the protruding mandrel end can be used to hold the sub-assemblyin a jig or chuck. It should be noted that it is considered generallyadvisable that care be taken to prevent uptake of moisture by thegreen-cured disc; such tubesheet compositions (see the above cited U.S.Pat. No. 3,829,331) are considered hygroscopic.

(e) The green-cured disc is next "fired" or cured by heating thesub-assembly to degrade and/or remove the cement components and anyremaining suspension medium and to fuse together the glass or ceramicparticles in the disc to form a densified, unitary tubesheet member withwhich the fiber portions passing through it are bonded in sealingengagement. This is done by supporting the sub-assembly at the tubesheetperiphery in an open pyrex container, which in turn is fitted closelywithin a closed metal casing, connecting the casing to a vacuum pump andplacing the casing (and contents) in a furnace. The disc is heated,essentially by irradiation from and through the pyrex container, to atemperature of about 340° C. and kept at that temperature for about 2hours. It is next further heated in the same manner, for about 4 hoursat a final temperature which is about 15° above the glass transitiontemperature of the tubesheet material but well below the glasstransition temperature of the fiber material, and is then allowed to(slowly) cool. With the solder-glass type of tubesheet materialsdisclosed in the above cited U.S. Pat. No. 3,917,490, the finaltemperature will range from about 370° to about 400° C.

(f) A generally bell-shaped, aluminum or stainless steel member(11)--which in this instance may aptly be characterized as having theshape of an inverted funnel, by reason of comprising a tubular, upwardextending section (12)--is prepared for sealing engagement with thetubesheet. (The tubular extension (12) is prejoined by weld bead (39) tothe horizontal wall (40) or "top" of member (11). The "top" and sidewalls of (11) are shown formed as one piece, but could be separatepieces joined by welding.) The rim (13) of the lower portion of member(11) is immersed (with or without being preheated) in a body of moltentubesheet glass until the rim is essentially at the temperature (˜700°C., for example) of the glass, then carefully withdrawn, together with athin, adherent layer (14) of the glass, and allowed to cool slowly andevenly.

(g) The sub-assembly is supported (by the protruding mandrel end) withthe tubesheet in a horizontal position and the glass-coated rim ofmember (11) is positioned essentially as shown in FIG. 1-A. The rim (andthe adjacent wall section) of member (11) is induction heated by asurrounding, water-cooled coil of copper tubing connected to a source ofradio-frequency, alternating current (a Lepel generator, for example).The heating is controlled so that the glass (or ceramic) coating on therim and the portion of the tubesheet in contact with it reaches thesintering temperature of the glass. This temperature is maintained untilthe rim of member (11) has slightly penetrated the tubesheet and thenthe resulting seal is allowed to cool slowly. The anolyte (or catholyte)tank has now been formed.

(h) The sub-assembly is next subjected to a helium leak test todetermine whether any fibers have been broken or the tubesheet iscracked. This is done with a commercial helium detector (a Varian, Model925-40, mass spectrograph unit which can detect helium flows as small as10⁻⁹ c.c. (measured at standard conditions) per second). The detector isconnected by rubber tubing to the tubular portion (the "funnel stem") ofthe tank and helium gas is passed through the mandrel and radiallyoutward, between the fibers and across the lower tubesheet face. If therate of helium flow through the detector is so low (<10⁻⁹ c.c./second)as not to be detectable, the sub-assembly is considered leak-free. (Atypical helium flow when a leak results from imperfect bonding betweenthe tubesheet and a fiber is about 10⁻⁷ c.c./second.)

(i) Several heli-arc weld beads (15) are run (see the above cited U.S.Pat. No. 3,791,868) radially across the lower surface of coil (10)between the periphery of the surface and its juncture with theprotruding portion of the mandrel, thereby locking the coiled foil skirtand tape wraps together and providing better electrical continuity tothe mandrel. The protruding portion of the mandrel is then melted offjust below its junctures with the inner ends of the weld beads.

(j) A perforation (17) is made through the skirt (6) of each wrap ofribbon (5), along each of several horizontal axes, by passing a needlepoint through the successive wraps along radii of the fiber/ribbonbundle between the closed fiber ends (4) and the upper edge of tape (7),thereby providing for subsequent charging of a liquid catholyte (oranolyte) to the spaces between the fibers not occupied by the ribbonwraps (5).

(k) A strip of foil, which may be a free end of the spacer tape or aseparate length thereof, is heli-arc welded to the coil (10) in suchmanner that it hangs freely from but is solidly connected thereto. Thedependent strip now constitutes a limp connecting link (16) and theinner assembly (18) is essentially complete.

(l) The inner assembly is lowered into a stainless steel casing sleeve(19). The sleeve is open at both ends and includes a tapered wallsection (20) which is intermediate of an upper, generally cylindricalwall section (21) of greater diameter and a lower, generally cylindricalsection (22) of reduced diameter, thereby defining a generallyfrusto-conical inner surface (23). The assembly is lowered until the(conforming) peripheral surface (24) of the tubesheet (9) rests onsurface (23). A stainless steel casing top wall (25), to which aninsulating seal (indicated generally as 26) and a stainless steel tube(27) have been joined by weld beads (28) and (29) respectively, isslipped down over the tubular section (12) of member (11). The innerassembly is raised until tubesheet surface (24) is spaced apart fromsurface (23) a distance which is sufficiently less than the radialdistance between the outer wrap of ribbon (5) and the casing wall (22)so that any lateral motion of the inner assembly will be stopped bycontact between surfaces (23) and (24) before any portion of theassembly below the tubesheet touches the casing side wall. (The spacingbetween the latter surfaces should, however, be large enough toaccommodate motions resulting from expansion and contraction of the cellcomponents, and this in turn limits how closely the inner assembly fitsin the lower part of the casing.) Weld bead (30), joining the casing topand side wall (25 and 21, respectively) is then formed.

(m) The upper part (36) of seal (26)--which is sized to fit closelythereto--is welded to the tubular section (12) of member (11), bead (31)being so formed. The inner assembly is thus suspended from the top wallof the casing; the upper end (32) of tubular section (12) and tube (27)are each adapted to function as both a fill port and an electricalterminal of the cell.

(n) The lower end of the foil strip (16) is welded to a stainless steeldisc (casing bottom wall, 33). The strip is folded, without beingcreased, and disc (33) is welded to side wall section (22), bead (34)being formed. The unfilled cell (35) is now essentially complete.

(Seal 26 is prefabricated and consists of upper and loweriron/nickel/cobalt alloy (KOVAR®) tubes (36 and 37, respectively) bondedto a hard glass insulator (38). Seals of this type have been obtainedfrom Larson Electronic Glass Company, Redwood City, Calif.)

(o) Introduction of anolyte and catholyte to a cell of the type shown inFIGS. 1-1B may be illustrated by the following procedure, used when theanolyte is liquid sodium metal, disposed inside the fibers, and thecatholyte is a liquid sulfur/sodium polysulfide solution disposedoutside the fibers. The cell is first tested for leaks, essentially inthe above described manner in which the sub-assembly was tested (step(h)), but with the helium being introduced through tube (27). It is thentested for internal shorts, transferred to a dry box, placed in asuitable heater and heated to a temperature within the range of120°-150° C. The tubular section (12) of member (11) is utilized toevacuate the anolyte tank (defined by member (11) and tubesheet (9)), tocharge molten sodium to the tank, and to repressurize it with an inertgas (Argon) to ensure complete filling of the fibers. Tube (27) isutilized to introduce molten sulfur to the space between the anolytetank and the casing, wherein it runs down to the bottom of the casingand rises within the fiber bundle, through perforations (17), andoutside the bundle, to a level sufficiently below the top of the core(3) to allow for the increase in catholyte volume which will result frompassage of sodium through the fiber walls during discharge of the cell.

(Although sulfur is a very poor electrical conductor, it is notnecessary to include any ionizable solute or conductive solids with itin order to initiate discharge of a hollow fiber type sodium/sulfurbattery cell. Sulfur is a sufficiently good conductor and the sulfurlayer between the fiber walls and the cathodic current collector is thinenough so that the cell can be started up simply by connecting it (at anappropriate operating temperature, such as ˜300° C.) to an externalload. The internal resistance will initially be high, but will decreaseas discharge progresses. Thereafter, the cell ordinarily will not berecharged to such an extent that the catholyte does not comprise asubstantial amount of sulfide.)

(p) The anolyte tank and casing can now be separately sealed by closingthe ends of tubes (12) and (27), respectively. The magnitudes and signsof the pressure differentials across walls (11) and (21), after sealingis complete, obviously will depend on the pressure conditions maintainedinside and outside of the (anolyte) tank when the closures are effected.Either space may be partially or wholly evacuated or may be pressurized(at the normal working temperature of the cell) with an inert gas. Aconvenient closure method, when the seal is to be made at ambientpressure, is to braze or solder a pre-tinned plug in the tubing end. Ifthe sealed space is to be held under sub-ambient pressure, the tubingmay be closed by pinching it off while connected to a source of vacuum,and then soldered in addition.

The order of the last several steps in the preceding sequence can bevaried and some of the steps can be modified, particularly if the casingused is of essentially constant diameter from top to bottom. For example(referring still to FIGS. 1-1B), if care is taken to ensure properpositioning, the sub-assembly consisting of members (25), (26) and (27),can be sealed to the tube (12) before the (inner) assembly is disposedin the casing sleeve. When this is done, the assembly may be supportedeither at the upper end (32) of tube (12) or at the tubesheet edge andthe sub-assembly supported in such manner that it is free to move asnecessary to accommodate any minor misalignment that occurs duringformation of the sealing bead (31).

Similarly, if the diameter of the lower casing section (22) is at leastas large as the diameter of the upper section (21), the sub-assembly(25)-(27) can be first welded to the casing sleeve (19) and then theinner assembly drawn (by means of a suitable tool releasably engagedwithin tube (12)) into the casing sleeve at its open bottom and up intoposition; bead (31) then being formed. If desired, bottom wall (33) canbe welded to (or otherwise conductively engaged with) the lower end oftape length (16) before the assembly is drawn fully into the casingsleeve.

The latter alternative can also be varied so that the assembly ispositioned within the sleeve, the casing bottom is joined to the end oftape (16) and then welded to the sleeve end, and the sub-assembly(25)-(27) is lowered into place (around an extension of the tool engagedwithin tube (12)) at the top of the sleeve and welded thereto. Bead (31)is then formed.

Step (j) can, in effect, be carried out before step (a), by selecting asthe foil ribbin one which is perforated at spaced intervals along a linea little further from the ribbon edge than the width of the spacer tape.(The foil also may be perforated in any desired pattern "above" thelatter line.)

Turning now to the cell of FIGS. 2 and 2A, elements 41-80 generallycorrespond to elements 1-40 in FIGS. 1-1B. The lower portion of theinner assembly is formed in essentially the same manner from a "ladder"of foil strips (41) and fiber lengths (42) having open and closed ends(43 and 44, respectively), a wide, carbon or MoS₂ -coated foil ribbon(45), a spacer tape (47) and a hollow metallic core (48). The coil(generally indicated as element (50)) is formed of the alternating wrapsof the foil skirt (46) and tape (47). The lower end (76) of the coreprotrudes from the coil and is solidly connected to it by radial weldbeads (55) across the lower surface of the coil. The upper end of thecore (48) is locked to the lower end of a non-conductive tube (77) whichextends through the tubesheet (49) and includes a necked-in section (78)with which the tubesheet is fused. The tubesheet constitutes the bottomof a carboy-shaped, non-conductive tank (indicated generally as 81)having side walls (51) and a top-wall (80) terminating in a neck (52).The tube (77) includes a (hollow) upper section (82) which extendsthrough and is sealingly engaged with each of necks (52) and a metalliccasing top wall (65). The portion of tube section (82) within tank (81)is foraminous and contains a metallic conductor (83) which extends, insealing engagement therewith, through the top end of tube section (82);the protruding portion (72) of conductor (83) constitutes a first(anodic) terminal of the cell. Tube (67) is joined by weld bead (69) tocasing top (65); it is closed at the top and constitutes a second(cathodic) terminal of the cell. The casing top (65) is joined by weldbead (70) to the upper section (61) of the casing sleeve (indicatedgenerally as element 59) and the lower section (62) of the sleeve isjoined by weld bead (74) to the bottom wall (73) of the casing. Theperipheral surface (64) of the tubesheet (49; i.e., the tank bottomwall) is spaced apart from the inner surface (63) of an intermediate,frusto-conical section (60) of the casing side wall or sleeve (59). Asoft wad (56) of a conductive fiber, such as graphite or carbon-coatedaluminum, is disposed in light contact with each of coil (50), core end(76) and casing bottom (73) and is immersed in a body (84) of arelatively low-melting sodium polysulfide, such as Na₂ S₅, disposed atthe bottom of the casing. Tank (81) (and the fiber interiors--notseparately numbered) contain a body (85) of sodium metal. The normalworking locus of the catholyte, i.e., the spaces between the fibers (42)and the foil wraps (45) and the "dead" space between the outermost foilwrap and the adjacent portion (62) of casing (59), contain a body (86)of sulfur or sodium polysulfide and are connected by perforations (57)in the foil skirts (46). The interior of the metallic core section (48)communicates through its open end, with polysulfide liquid (84).

The procedure for assembling the cell of FIGS. 2 and 2A is generally thesame as that described for the cell of FIGS. 1-1B. However, certain ofthe steps differ in several respects.

In step (b), the mandrel on which the fiber and foil "jelly-roll" ofFIGS. 2, 2-A is formed, and from which core (48) is derived, includesnot only a lower extension which protrudes from the bottom of the jellyroll and is later cut off, but is also crimped at its upper end around aconforming lower end of a tube (77) which has been preformed with anintermediate, necked-in section (78) and a foraminous upper section (82)and consists of the same material as the particles in the tubesheetpaste. Section (78) is necked-in as much as possible, i.e., until thetube interior is closed off at that point, in order to avoid cracking atthe tubesheet and tube juncture as a consequence of shrinkage when thetubesheet disc is dried and cured. For the same reason, the sizedistribution for the solid particles in the tubesheet paste iscontrolled (in accordance with well-known principles) to minimize theliquid vehicle content therein and to maximize the packing density inthe disc after it has been "green cured" in step (c).

Step (f) is omitted, since the generally bell-shaped member (51) ispreformed from the same material as the tubesheet and its rim (53) doesnot have to be coated with glass.

Step (g) is essentially unchanged but the rim of member (51) simplybonds with the peripheral portion of the tubesheet and any "penetration"which occurs will be insignificant.

Neck (52), appropriately sized to fit closely to tube section (82), isfused to it (as with a carbonmonoxide torch) to form a ring joint (79)of a well known type. This joint corresponds to the preformed weld bead(39) in the cell of FIGS. 1-1B.

Step (k) is omitted, since the limp link will be provided subsequently,i.e., in a modification of step (n).

The sealing operations of steps (l) and (m) are modified. Seal (71)includes a glass to metal joint which is formed after conductor (83) isdisposed in tube section (82), following introduction of (molten) sodiumto tank (81) through tube section (82). The latter conductor preferablyis easily deformable and is coated below its upper end (72) with a beadof the tubesheet glass before being inserted in tube section (82). Theseal (71) is then completed between the bead and the adjacent portion oftube section (82,) by heating, and allowed to cool slowly. The conductorcan be placed in the tube section and seal (71) formed before the"jelly-roll" is built up on the mandrel, if the portion of tube section(82) between seals (66) and (71) is first joined to a glass sideextension which can later be used as a sodium fill port and then closed.Seal (66) also includes a metal to glass joint and preferably is madebefore top wall (65) is welded to the casing sleeve. The seal is made byforming an appropriate opening in top wall (65), coating the lip of theopening with tubesheet glass, positioning the top wall with respect totube section (82) and completing the seal by fusing the coating with thetube wall.

Next, top wall (65) is welded to the upper casing sleeve section (61),bead (70) being formed.

Step (n) is modified by placing the soft fiber wad (56) between casingbottom (73) and the lower surface of the coil (50) and welding thebottom (73) to the lower casing sleeve section (62). The wad is sized tobe under very slight compression when so enclosed and functionssimilarly to the tape end (16) which is the limp link in the cell ofFIG. 1A. As shown in FIG. 2A, the voids within the fiber wad areoccupied by a polysulfide material, such as Na₂ S₅, which melts at atemperature (˜252° C.) well below the contemplated operating temperature(˜300° C., for example) of the cell.

The fibers constituting the wad are not joined to the bottom of the coilor to the casing bottom and the polysulfide will not function to anysubstantial extent as an electrical conductor. However, the contactbetween the wad and the metal surface above and below it will beadequate and it is preferable that the void spaces in the wad be filledby polysulfide, rather than by sulfur.

Step (o) is modified to the extent that the polysulfide (84) isintroduced (through tube (67)--not yet closed) to the casing interiorbefore the sulfur (86) is introduced.

Several variations can be made in the cell of FIGS. 2 and 2A. The majorportion (82) of tube (77) which is above the tubesheet can be a lengthof metal tubing engaged with the upper end of a somewhat extendednon-conductive intermediate portion of tube (77). Also, the core (48)itself may be non-conductive; that is the core may simply be a downwardextension of the (non-conductive) section of tube (77) which passesthrough the tubesheet.

If the upper tube section (82) is made of metal, conductor (83) iseliminated and seal (52) is no longer a simple glass-to-glass ring jointbut is made by first forming a glass collar on the metal tubing and thenfusing the collar to neck (52). Seal (71) is replaced by a simple metaltube closure and seal (66) can be the insulating type of seal (26) usedin the cell of FIGS. 1-1B. It is of course necessary, in the lattercase, to engage the upper and intermediate sections of tube (77) in suchmanner (a sliding engagement, for example) that the length of the metalsection can change to a limited extent without stressing the tubesheet(etc.). This requirement can only be met so long as the tubesheet doesnot sag substantially below its original position. Accordingly, thisvariation is considered less desirable for larger diameter cells inprolonged service.

In another variation, the portion of tube section (82) within theanolyte tank is eliminated and the rest of tube section (82) is simply(is replaced by) an upward tubular extension of the neck (52) of member(51). The latter extension is closed at its top (outer) end and engagedwith the top (72) of conductor (83) by seal (71).

Referring now to FIGS. 3-3C, the elements of the cell shown arecataloged below. Elements 91-117 correspond to elements 1-27 in FIG.1-A.

    ______________________________________                                        Element                Number                                                 ______________________________________                                        Aluminum foil strips    91                                                    Hollow fiber lengths    92                                                    Open fiber ends         93                                                    Closed fiber ends       94                                                    Lengths of wire         95                                                    Lower end portions of wire lengths                                                                    96                                                    Wraps of spacing tape   97                                                    Aluminum core of square cross-                                                                        98                                                    section, closed at both ends                                                  Tubesheet               99                                                    Tape and wire-end coil 100                                                    (indicated generally)                                                         Inverted, funnel-shaped, aluminum cup                                                                101                                                    Upward extending tubular portion                                                                     102                                                    of cup                                                                        Rim of inverted cup    103                                                    Coating of glass on rim, fused                                                                       104                                                    to tubesheet                                                                  Anolyte tank (indicated generally)                                                                   105                                                    Metal sleeve around fiber (etc.)                                                                     106                                                    bundle                                                                        Metal disc welded to bottom of tape                                                                  107                                                    coil                                                                          Inner assembly (indicated generally)                                                                 108                                                    Glass or ceramic casing side walls                                                                   109                                                    Intermediate section of casing side                                                                  110                                                    wall                                                                          Interior surface of element 109                                                                      111                                                    Peripheral surface of tubesheet                                                                      112                                                    Casing top wall        113                                                    Seal (top)             114                                                    Fill port              115                                                    Conductive metal disc  116                                                    Metal tubing length    117                                                    Weld bead              118                                                    Casing bottom wall     119                                                    Seal (bottom)          120                                                    Silver solder bead     121                                                    Glass/metal joint      122                                                    Weld bead              123                                                    Negative cell terminal (on                                                                           124                                                    discharge)                                                                    Positive cell terminal (on                                                                           125                                                    discharge)                                                                    Cap closure at lower end of core                                                                     126                                                    Thin layer of powdered, low                                                                          127                                                    melting metal                                                                 Perforations through catholyte cup                                                                   128                                                    wall                                                                          The complete cell (indicated                                                                         129                                                    generally)                                                                    ______________________________________                                    

The procedure for assembling the cell of FIGS. 3-3C is similar to theprocedure outlined for the cell of FIGS. 1-1B, but differs as follows.

In step (a), the conductive sheet is replaced by a plurality ofgenerally parallel lengths (95) of wire, such as molybdenum wire or analuminum wire coated with carbon or MoS₂. The lower ends (96) of thewire lengths, which extend across spacer tape (97) in the "ladder" ofFIG. 3-C, differ from the foil "skirts" (6) in FIG. 1-A in an obviousmanner and the rolled up coil (100) is a more open structure. Also, notape end is provided, since other means are used to provide a limp link(127).

In step (b), the mandrel (from which core (98) is derived) is closed atthe upper end, is square in cross-section and is sufficiently large in"diameter", in comparison to the fiber size, and the number of wraps inthe "jelly-roll" are such, that the roll generally retains the squarecross-section (see FIG. 3B). Since there is no foil wrap around theroll, a somewhat stiff, metal sleeve (106) of square cross-section,sized to fit closely to the roll, is very carefully slipped up aroundthe roll to protect the fibers and to subsequently limit upward motionof the coil, core, etc., relative to the tubesheet.

Step (i) is modified in several respects. The heliarc weld beads (notshown) are extended to join with the lower edge of sleeve (106). Then asquare, conductive metal disc (107; see FIG. 3A) having a square hole atthe center is slipped onto the protruding mandrel end (not shown),raised up against the coil bottom and welded to both the mandrel and thesleeve (106) (weld beads not shown).

The protruding portion of the mandrel is cut off a short distance belowcoil (100) and the stub is covered with a shallow square cap (126) whichis then welded around its periphery to disc 107. (The hollow core isessentially empty (evacuated of gas-filled) and provides buoyancy, aftercatholyte is charged to the cell, to counteract the weight of the corematerial, coil and wires; the distance between the top of the core andthe tubesheet is less than the distance between the closed fiber endsand the coil but is somewhat greater than the distance from thetubesheet periphery to the top edge of the sleeve (106)).

In step (j) there are no foil wraps to perforate but perforations (128)are made through sleeve (106) at a level between the closed fiber endsand the coil, to permit entry of catholyte to the fiber (etc.) bundleeven when the top edge of sleeve (106) is in contact with the tubesheet.Step (k) is omitted.

Steps (l) and (m) are modified in several respects. The casing consistsof glass or ceramic and the casing top wall (113) is fused to the casingside walls (109) and the top seal (114) is joined to the top wall (113),before the inner assembly (108) is disposed in the casing. The latterassembly is drawn--by a suitable tool releaseably engaged with theinterior of tubular section (102)--into the casing at its bottom and upinto position such that the upper end (124) of member (102) protrudes apreselected distance above seal (114). Care is taken in this operationto ensure that the core, coil (etc.) does not move further from thetubesheet and that the vertical axes of members (102) and (114) areessentially coincident. The latter two members are joined by a weld bead(123). (Seal (114) includes a glass to metal joint (118) formed byprecoating the lower lip of the seal with glass and then fusing theglass to the casing top wall (113).)

The lateral spacing between the tubesheet peripheral surface (112) andthe interior surface (111) of sidewall section (110) is substantiallyless than the spacing between the sleeve (106) and side walls (109),thereby ensuring that gross lateral motion of the inner assembly will bearrested before the fibers are subjected to any torque, withouthindering expansion/contractive motions.

In step (n), the bottom wall (119) of the casing is fused to thesidewalls (109) before the limp link is formed. First, however, lowerseal (120) is joined (as above) through a glass to metal joint (122) tobottom (119), and tubing length (117) is joined by weld bead (118) tometal disc (116) and inserted through the seal as shown. Then the casingbottom is joined to the casing walls and the limp link is formed byintroducing a sufficient amount of powdered metal particles through fillport (115) (and shaking them down) to form (when melted) a thin, liquidlayer contacting both the coil (100) and the disc (116).

The unfilled cell (indicated generally as (129)) is now complete and maybe charged with catholyte (through fill port (115)), the space betweenthe casing and the sleeve (106) and through perforations (128) near thebottom of the sleeve. As the catholyte level within the fiber (etc.)bundle rises, the closed, hollow core (98)--if or sufficientvolume--will tend to rise, taking with it the wires, the coil (100),sleeve (106) and disc (107). However, the top edge or rim of sleeve(106) will--by design--contact the tubesheet bottom before the top ofthe core does (even through the core has expanded to the length it hasat the working temperature of the cell). This disposition will not bealtered when the catholyte volume is further increased, either by addingmore catholyte initially or by discharging the cell. Optionally, thecore may be so sized and positioned and made of such a material that,when it is fully expanded, its top is so close to the tubesheet that anysubstantial sagging of the tubesheet will be resisted by the net buoyantforce on the core.

After the catholyte is charged to the cell, port 115 may be fused shut.

The tubular extension (102) can be used as a fill port for introductionof anolyte to the cell and then closed. The upper portion (124) ofmember (102) then will function as the upper cell terminal (the negativeterminal, on discharge, for example). The lower portion (125) of tubinglength (117) will function as the lower (+) terminal of the cell and maybe left as shown or closed.

Turning finally to FIG. 4, the elements numbered 131-148 correspond toelements 1-17 in FIG. 1-A. All of the cell elements are cataloged in thelist below.

    ______________________________________                                        Element                Number                                                 ______________________________________                                        Aluminum foil strips   131                                                    Fibers                 132                                                    Open fiber ends        133                                                    Closed fiber ends      134                                                    Wraps of foil ribbon   135                                                    Skirt portions of (135)                                                                              136                                                    Wraps of spacer tape   137                                                    Core (indicated generally)                                                                           138                                                    Tubesheet              139                                                    Coil (generally indicated)                                                                           140                                                    Inverted anolyte cup   141                                                    Sodium fill port (closed)                                                                            142                                                    Rim of anolyte cup     143                                                    Glass coating          144                                                    Conductive metal disc at coil bottom                                                                 145                                                    Limp (metal foil) link (bottom)                                                                      146                                                    Limp (metal foil) link (top)                                                                         147                                                    Perforations in foil skirts (136)                                                                    148                                                    Metallic section of core (138)                                                                       149                                                    Non-conductive section of core (138)                                                                 150                                                    Necked-in upper end of (150)                                                                         151                                                    Necked-in lower end of (150)                                                                         152                                                    Crimped end of (149)   153                                                    Perforations in (149)  154                                                    Sulfur                 155                                                    Plug in upper end of (149)                                                                           156                                                    Cap                    157                                                    Lower casing section   158                                                    Flared and radiused rim of (158)                                                                     159                                                    Shoulder               160                                                    Thickened lip of hole in bottom of                                                                   161                                                    lower casing section (158)                                                    Tubing length (metal)  162                                                    Glass coating on end of (162)                                                                        163                                                    Rod                    164                                                    Bulge near end of rod  165                                                    End closure            166                                                    Connection plate       167                                                    Sodium                 168                                                    Upper casing section   169                                                    Flared and radiused rim of (169)                                                                     170                                                    Thickened lip of hole in top of (169)                                                                171                                                    Tubing length (metal)  172                                                    Glass coating          173                                                    Rod                    174                                                    Bulge near end of rod  175                                                    End closure            176                                                    Connection plate       177                                                    Bulged equitorial casing joint                                                                       178                                                    (indicated generally)                                                         Sleeve around fiber (etc.) bundle                                                                    179                                                    Inner assembly (indicated generally)                                                                 180                                                    Completed casing (indicated generally)                                                               181                                                    Completed cell (indicated generally)                                                                 182                                                    ______________________________________                                    

The procedure for assembling the cell of FIG. 4 corresponds generally tothat described for the cell of FIGS. 1-1B. The same type of (cathodic)current collector, a wide ribbon of foil, is employed. The core (138)comprises a lower, metallic section (149) and a pre-formed,non-conductive upper section (150) having necked-in top and bottom ends,(151) and (152) respectively. The upper end (153) of core section (149)is crimped around the lower end (152) of core section (150).

In step (a) of the procedure, the spacer tape does not include a freeend, since a separate tape length will subsequently be provided to formlimp link (146).

In step (b), the protruding portion (not shown) of the mandrel andsection (149) of core-to-be (138) are contiguous and are open from thecrimped end (153) down. The bead of tubesheet paste is started at theupper end (151) of the mandrel so that the tubesheet will be integralwith the non-conductive core section (150).

Step (f) differs in that the (inverted) anolyte cup (141) is notextended by a tubular section which is to pass through the cell casing.Instead, a tube length (not shown as such) which will function as a fillport and then be pinched off and closed to form element (142), isextended from the "top" of cup (141).

The sequence of steps (i) and (j) is reversed. That is, perforations(148) through the foil skirts (136) are formed before step (i) iscarried out.

In step (i), after the heli-arc weld beads (not shown) have been formedacross the bottom of the coil (140), a metal sleeve (179) is slipped uparound the outer wrap of foil ribbon (135). Then a metal disc (145)having an appropriately shaped hole at the center is slipped onto theprotruding mandrel end (not shown), raised up against the coil bottomand welded to the mandrel and to the lower edge of the sleeve (weldbeads not shown), thereby forming a fluid-tight catholyte cup (notseparately numbered).

In step (k) two soft metal tape lengths, (146) and (147) respectively,are welded at one end to the top of the anolyte cup (141) and to disc(145), as shown.

Step (o) is now performed out of sequence. That is, the anolyte andcatholyte cups are filled before the casing is formed around the innerassembly. The assembly is supported at the tubesheet periphery and aheating coil, consisting of two, hinged sections enveloped ininsulation, is closed around each of the cups (within an enclosurehaving an inert atmosphere and equipped with remote manipulator). Moltensodium is charged through the fill tube (not shown as such), which isthen largely removed and the remaining stub (142) fused shut as shown.

The protruding mandrel end (not shown) is connected to a source ofmolten sulfur (for example), which is then caused to flow, in apredetermined amount, up through the mandrel, out through perforations(154), down between the mandrel and the adjacent wrap of the foilribbon, horizontally through perforations (148) and up through thespaces between the fibers and ribbon wraps, to a level slightly aboveperforations (154). The sulfur source is depressurized and the mandreldrained until no more sulfur can flow back into perforations (154).

The mandrel end is cut off a little below disc (145) and aclose-fitting, graphite-coated, aluminum, sealing plug (156) is pushedup through the mandrel (now the core (138)) to a level just belowperforations (154). A shallow cap (157) is then placed over the mandrelstub and soldered or laser welded (bead not numbered) to disc (145).Since core section (149) now contains a trapped body of (inert) gas, nocatholyte can enter it.

The inner assembly is now not only complete, but is also charged withanolyte and catholyte--which are kept molten throughout the rest of thecell assembly procedure.

Step (n) is completed before steps (l) and (m). That is, the limp linksare connected to the casing (halves) before the inner assembly isdisposed therein. Each of casing "halves" (158) and (169) is end-fittedwith an open length of aluminum tubing, (162) and (172) respectively(which will function as terminals of the cell) in the following manner.An appropriately sized hole, the lip (161) of which is thickened andbulges out, is formed in the bottom wall of the lower casing "half"(158). Tubing length (162) is dipped in molten glass (the same materialthe casing consists of, for example) to form a coating (163) and isinserted in the hole and sealed in place by fusing the glass coating tothe lip of the hole. (Tubing length (172) is likewise provided with anend coating (173) and sealed in place in the top of casing half (169) byfusion of the coating with lip (171).)

An electrical connection between each of tubing lengths (162) and (172),respectively, and the free ends of tape lengths (146) and (147), is madenext (the tapes being extended to full length). A metal rod (164) with apreformed, annular bulge (165) near one end is welded at the other endto a metal disc, or end-closure (166) and inserted in tubing length(162) as shown. The disc (166) is edge-welded to the end of tube (162).A connecting plate (167) having a hole at its center is slipped onto theend of rod (164), against bulge (165) and spot-welded to the adjacentrod end. A hole is punched in the free end of tape (146), which is thenslipped over the rod end and welded to it (and to plate (167)). In thesame manner, the sub-assembly of elements (174)-(177) is formed andconnected to elements (172) and (147), to complete the anodic connectionwithin casing "half" (169). A limp connecting link has now been formedat each end of the (as yet not fully assembled) cell.

Cell assembly steps (l) and (m) are completed as follows. The heatingcoil around the anolyte and catholyte cups are removed, the support atthe tubesheet edge is removed and the lower casing "half" (158), whichhas a flared and radiused rim (159) defining a shoulder (160), and hasbeen pre-heated, is immediately brought up around the catholyte cup(tape (146) being carefully folded in the process) until the shoulder(160) bears against the tubesheet periphery. The (preheated) uppercasing "half" (169) which also has a flared and radiused rim (170), isimmediately brought down around the anolyte cup (tape (147) beingcarefully folded in the process) until the rim (170) makes flush contactwith the rim (159). The two casing halves are then joined by fusing rims(159) and (170) together, to form an equatorial bulge (178), defining agroove (unnumbered) in the side wall(s) of the casing (indicatedgenerally as (181)) in which the peripheral portion of the tubesheet is"trapped". It is not necessary that a bond be formed between thetubesheet and casing. In fact, the tubesheet edge preferably isprecoated with a non-fluxing lubricant, such as graphite, to preventsuch bonding, thereby minimizing the likelihood of residual stresses onthe completed joint.

The completed cell should be kept hot enough to maintain the catholyte(the sulfur, for example) molten. Otherwise, fiber breakage may occur.For this reason, assembly of a complete cell of the latter type may bedeferred and done at the location where the cell will be used. However,a heating coil, powered by the battery itself or by a separate source ofelectrical power, may be used--in combination with an insulatedcontainer--to keep the cell hot while it is being transported.

Again, the distance between the casing and the anolyte and catholytecups is, at all locations, substantially greater than the radialdistance the tubesheet can move before its motion is arrested at thesurface of the groove it is disposed in.

At this point, it is apparent that the cell of FIG. 4 can be modified sothat the inner assembly is engaged with the casing at the bottom, ratherthan at the tubesheet periphery. This is done by passing the protrudingmandrel end--which is not cut off in this embodiment--through, and insealing engagement with, the casing bottom. The limp link at the top ofthe assembly is retained. The lower end of the mandrel serves thepositive terminal of the cell and as a (sulfur) fill port. Thismodification is possible because the upper (non-conductive) end of themandrel (the core) is engaged with the tubesheet and the weight of theassembly will not stress the fibers. To avoid substantial stressing ofthe fibers as a consequence of expansion by the lower (metallic) portionof the core, this portion is shortened. That is, the non-conductiveportion is extended down to a level somewhat above the lower surface ofthe tape coil. Since alternative cathodic connecting means may readilybe employed at the cell bottom, the mandrel may even be made entirely ofa non-conductive material. The joint between the two casing sections canbe made at the juncture between the top wall and the side walls, ratherthan as an equatorial joint, the inner assembly being lowered into placeand engaged with the casing bottom before the upper end of the foilstrip (the limp link) is connected to the terminal post in the casingtop and the top is joined to the rest of the casing.

It is also apparent that in the cell of FIG. 4 substitution of a steelwool felt or wad, or a liquid metal, for at least the bottom limp link,would be facilitated by the fact that the catholyte is contained in acup.

DEFINITION OF THE PROCESS INVENTION

The essential steps in the method of the present invention are thosewhich are indispensable to forming a hollow fiber type, high temperaturebattery cell in which (1) an element of an inner assembly comprising thefibers is so engaged with (a wall of) a surrounding, fluid-tight casingthat motion of the assembly within the casing is limited but saidengagement does not hamper expansive/contractive motions of the assemblycomponents, and (2) at least one of the electrical connections betweenthe assembly and the casing terminals comprises a limp link.

Thus, the first essential step (I) is to provide an inner assemblycomprising an element which is so incorporated therein and extendstherefrom in such manner that it can be engaged with the casing so as tosupport and position the assembly therein, without thereby causing theassembly to otherwise contact the casing in a manner which imposes astress on any element of the assembly or which will result in suchstressing if thermally induced dimensional changes subsequently occur inthe assembly. A second essential step (II) is to so engage the innerassembly with the casing. A third essential step (III) is to completethe necessary connections between the casing terminals and the anode andcathode of the inner assembly, by means of as many (one or two) limplinks as are required.

Before the cell is put into use, such seals as are required to preventcontact of the anolyte and catholyte will each other or with theatmosphere external to the cell will be formed. Of course, thisrequirement is not novel to cells of the present invention. However,sealing may be an essential part of the operation in which the necessaryengagement between the inner assembly and the casing is effected.

In the procedures described herein for assembling the cells of FIGS.1-4, the essential steps I-III set out above may be identified asfollows:

    ______________________________________                                                 Sequence of Essential                                                                           Corresponding                                      Cell of  Steps of Method   Alphabetical                                       FIG. #   of Invention      Sequence Steps                                     ______________________________________                                        1        I                 a through j                                                 II                l and m                                                     III               k and n                                            2        I                 a through e                                                                   and g through j                                             II                l, m and n                                                  III               n                                                  3        I                 a through j                                                 II                l, m and n                                                  III               n                                                  4        I                 a through i,                                                                  and o                                                       III               k and n                                                     II                l and m.                                           ______________________________________                                    

It is apparent from the preceding tabulation that steps II and III maybe carried out in whichever order is appropriate to the particular typeof cell being assembled. That is, the method invention comprises step Ifollowed by one of steps II and III and then by the other.

More precisely, the method of the invention may then be defined as:

A process for fabricating an essentially stress-free battery cellcomprising a closed casing having two external electrical terminals andan inner assembly disposed within said casing and electrically connectedto said terminals,

said process comprising steps I, II and III as defined below, in eitherof the sequences I, II, III or I, III, II;

I. providing, as said assembly, an assembly which includes (1) aplurality of hollow fibers adapted to function as theelectrolyte/separator in a battery cell and (2) an element soincorporated in and extending from said assembly that it can be engagedwith said casing to support and position the assembly therein withoutthereby causing the assembly to otherwise contact the casing in a mannerwhich imposes a potentially damaging stress on any part of the assemblyor which will result in such stressing if thermally induced dimensionalchanges occur in the assembly;

II. so engaging said element with said casing, and

III. forming a separate, electrical connection from each of saidterminals to said assembly, at least one of the connections comprising alimp link.

Suitable materials of construction for the cells of the presentinvention are generally known to those skilled in the electrochemicalarts. However, the material requirements for certain components ofsodium/sulfur battery cells will be summarized.

Suitable materials for the cathodic current collecting means in the cellare otherwise suitable electrically conductive metals which can befabricated as sheets of foil, screening or wires and, as such as whencoated with carbon, MoS₂, molybdenum or chromium metal, etc., do notdevelop a high surface resistance on prolonged contact with moltensodium polysulfides. Exemplary of such metals are aluminum, aluminumalloys, stainless steels, molybdenum, iron, etc.

Suitable "limp link" materials for use in the present invention areelectronically conductive liquids or are solids capable of being formedas a folded foil or soft wool which exhibits essentially no resistanceto changes in shape or position. Also suitable are slurries orsuspensions of conductive solid particles in liquids which are at leastcapable of ionic conduction.

Not only graphite or metals may be used in the latter manner, but alsocharge transfer complex compounds. U.S. Pat. No. 4,071,662 discloses theuse of vinyl pyridine polymer/iodine charge transfer complexes ascathode components in lithium-iodine batteries. British Pat. No.1,504,680 discloses charge transfer complexes between vinyl pyridinepolymers and iodine which exhibit metallic type electrical conductivityand are stable up to temperatures of at least 350° C. It is essentialthat the liquid component of the slurry be chemically inert (as definedearlier herein) to the particulate component.

The electrical path through the limp link should not substantiallydecrease in conductivity or cross-sectional area upon prolongedoperation of the cell. Therefore, in those cases where the link materialis a solid article immersed in the catholyte (or anolyte), the surfacesof contact between the link and the rest of the connecting meanscomprising it should be inaccessible to and not detrimentally reactivewith the surrounding catholyte (as when a foil is welded to an inner endof a terminal post. Also, such reaction as may occur elsewhere betweenthe link surface and the catholyte should be self-limiting, so that thecorrosion of the link does not proceed beyond formation of a surfacelayer of the resulting reaction product. It is of course necessary thata solid link be composed of a material which melts above thecontemplated operating temperature of the cell.

Suitable solid link materials are conductive, readily deformedsubstances which are essentially inert to or self-passivating in contactwith the catholyte (or anolyte). Metals which are ductile or which canbe formed as sufficiently soft wools are preferred such materials, butgraphite (wools) are also suitable--particularly when immersed inconductive liquids. Specific metals which may be employed as foils arealuminum or soft alloys of aluminum with cadmium, etc. According to U.S.Pat. No. 4,102,960, graphite may also be fabricated in the form of highstrength, flexible foils.

As indicated above, whenever the contact between the limp link and therest of the connecting means it is part of is not of such a nature as toprevent intrusion of a corrosive or poorly conducting liquid at thecontact interface, such intrusion must otherwise be prevented (as bycontaining the catholyte in a cup) or the contacting surfaces must beable to maintain their conductivity in the presence of the liquid.Coating of metal contact surfaces with carbon, MoS₂ or molybdenum metalis helpful when conductivity must be maintained in the presence ofsodium polysulfides.

Whether or not a particular type of conductive liquid will be suitableas a limp link depends on whether it will be in contact with thecatholyte (or anolyte) and its reactivity with the same. Thus,relatively low melting, conductive metals or alloys may be employed as alimp link between the cathode terminal of a cell and the bottom of ametallic catholyte cup, even though they are not inert, provided that nosubstantial contact between the catholyte liquid (or vapors) and thelinking liquid will occur. It is also necessary that the portions of theconnecting means (the cup bottom, for example) and the terminal incontact with the liquid metal be essentially insoluble in and notdetrimentally reactive with it.

Specific metals which are liquid and do not boil at the operatingtemperatures (˜300°-360° C.) of sodium/sulfur cells, for example, arecadmium, galium, indium, potassium, sodium, thallium and tin. Mercurymay be used at temperatures below ˜357°, its boiling point. Althoughsuch metals, for one reason or another, are generally not verypractical, their use, particularly in alloys--such as lead-tin solders,for example--is not ruled out.

Preferred as liquid components of slurries to be employed as limp linkmaterials are relatively low-melting salts or weak bases or acids.Specific low melting salts are aluminum bromide (m.p. 97.5° C., b.p.˜263° C. @747 mmHg); aluminum iodide (m.p. 191° C., b.p. 360° C.);arsenic triiodide (m.p. 146° C., b.p. 403° C.); arsenic trisulfide (m.p.300° C., b.p. 707° C.); bismuth tribromide (m.p. 218° C., b.p. 453° C.);bismuth trichloride (m.p. ˜231° C., b.p. 447° C.); metabasic acid (m.p.236° C.); boron trisulfide (m.p. 310° C.); boron pentasulfide (m.p. 390°C.); cadmium iodide (m.p. 387° C., b.p. 796° C.); chromium acetonylacetate (m.p. 216° C., b.p. 340° C.) and galium iodide (m.p. 212° C.,sublimes at 345° C.). Numerous other such salts, etc., are listed in theHandbook of Chemistry and Physics; The Chemical Rubber Co., Cleveland,Ohio; 45th edition, 1964-5. Particularly preferred for use insodium/sulfur cells is sodium pentasulfide (m.p. ˜252° C.). It will berecognized that some of the above-listed salts would react with thecatholyte in an alkali metal/sulfur cell, but that fact does not rendersuch salts unsuitable for use in other types of (hollow fiber) batterycells.

Although the foregoing molten salts are generally ion-conductive, theywill exhibit only minimal sustained conductivities as slurry componentsunder the existing potential drop available and a content in the slurryof about 25 weight percent or more of the electronically conductiveparticles will generally be required. Preferably, the solids content ofthe slurry will be as high as possible without loss of the fluiditywhich facilitates functioning of the slurry as a limp (readily deformed)link.

It is of course necessary, in designing a given cell wherein the limplink is or comprises a material which is liquid at the contemplatedoperating temperature, to consider whether or not that material expandsupon solidifying and, if so, to ensure that such expansion can occurwithout detrimentally stressing the inner assembly or the casing. Forexample, the catholyte may be held in a cup, the bottom of which isconically convex and the limp link material disposed as a thin layerbetween the cup bottom and a conforming (and conductive) interiorsurface of the casing, in an amount which does not fully occupy thespace between the conforming surfaces.

It is to be emphasized that only a quite thin layer of a liquid orslurry will be required to function as a limp link. (The thickness ofthe (powdered) metal layer (127) in FIG. 3A is exaggerated for the sakeof clarity in the drawing.) It is only necessary that such a fluid linkhave a thickness somewhat greater than the maximum elongation of theinner assembly which will result when the cell is heated to itsoperating temperature.

It is not necessarily required that a liquid or slurry type link beisolated from or even immiscible with the catholyte. In fact, a lower,"dead" portion of the catholyte (or anolyte) itself may, in the form ofa thin layer, serve, in admixture with conductive solid particles orfibers, as a limp link component. However, in all cases, it is essentialthat the liquid component be inert (as defined earlier herein) to suchcell components (the catholyte, for example) as it will be in contactwith under the operating conditions to be employed.

Suitable casing materials are those which are otherwise suitable and canbe fabricated in the requisite shapes, are resistant to corrosion by thecell contents which make contact with the casing, and with which therequisite joints or seals can be effected. In those embodiments in whichthe casing itself constitutes part of the electrical pathway between oneof the cell electrodes and a terminal, it is also necessary that thecasing material be adequately conductive. In this case, it ordinarilywill not matter if the interior surface of the casing forms anon-conductive or highly resistant layer on contact with the catholyte,since a bonded contact between the cathodic current collecting means andthe subjacent portion of the casing wall can generally be provided (asabove discussed).

Materials of the preceding general type are not necessarily limited to,but usually will be, metals, glasses or ceramics. Specific suitablecasing materials are stainless steel, carbon steel, aluminum or aluminumalloys, graphite, steel which has been surface treated with aluminumpowder at elevated temperatures, chrome or molybdenum plated steel andconductive or insulating ceramics.

Preferred among the latter materials are surface treated or coatedsteels, stainless steel or ceramic glasses.

Suitable anolyte and catholyte cup materials also are generally metals,glasses and ceramics. When an electrically non-conductive material, orone which develops a high surface resistance, is used as a cup, the cupitself of course cannot function as an electrical connecting means. Aseparate collecting means must then be provided or the cup surface mustbe coated with a material, such as carbon, MoS₂ or molybdenum orchromium metal, which resists formation of a poorly conducting surfacelayer.

Suitable mandrel/core materials are those which can be formed intoelongated, generally tubular members of the requisite rigidity and areadequately resistant to the catholyte (or anolyte). Again, metals,glasses and ceramics are generally suitable for this purpose. Althoughthe core may be electrically conductive and thereby function as part ofa current collecting or connecting means, this is not essential, sinceuse of a separate such means (i.e., a foil, for example) having a muchhigher surface area will usually be necessary. (In fact, once themandrel has functioned as such, and if it is removeably incorporated inthe fiber, foil, etc., bundle, it can be slipped out. Generally,however, it will be preferred not to do this.)

Suitable tubesheet materials are electrically nonconductive materialswhich have approximately the same thermal coefficient of expansion asthe hollow fiber or tubule material (see U.S. Pat. No. 3,917,490; column3, lines 48-55). The tubesheet material must of course be adaptable toat least one procedure by which a self-supporting, non-pervious disc ofthe material, having the fiber ends passing in sealing engagementthrough it, can be formed. Glasses and ceramics are known suitabletubesheet materials (see U.S. Pat. No. 3,672,995 and 3,917,490).

Suitable cation-conductive hollow fiber materials are disclosed in U.S.Pat. No. 3,672,995; 3,829,331 and 4,050,915. Other cation-conductiveglasses and ceramics are disclosed in numerous patents, of which U.S.Pat. No. 4,002,807 is exemplary.

The present invention may also be practised with anion conductivefibers. According to K. H. Stern, Glass-Molten Salt Interactions,Chemical Reviews, Vo. 66, No. 4, July 25, 1966, oxide and hydroxylanions are known to be mobile in glass at elevated temperatures andthere is evidence which suggests that fluoride ion may also be mobile attemperatures below those required to melt feldspar-containing glasses.

The inherent advantages of the hollow fiber electrolyte/separatorconfiguration are realized to a maximum extent with thin-walled, smallerdiameter (hairlike) hollow fibers. On the other hand, it is difficult tospin uniform fibers having outer diameters of less than about 30microns. Accordingly, fibers having outer diameters of from about 30 toabout 1000 microns and wall thicknesses of from about 0.04 to about 0.1of the outer diameter are preferred. However, hollow fibers havingdiameters as small as 7.5 microns are disclosed in U.S. Pat. No.3,268,313 and glass capillaries having diameters of up to about 6500microns would be expected to be subject to damage by thermal stressing,in inverse proportion to their wall thicknesses. Thus, hollow fiber typebattery cells in which the capillaries size ranges from the smallestfeasible diameters to about 6500 microns are considered within the ambitof the present invention.

An optional modification of cells of the types illustrated by FIGS. 1-3is to provide sufficient space between the anolyte tank casing tocontain the material normally disposed around the outside of the fibers.By altering the position of the cell, this material (the catholyte, forexample) may be drained out of its normal working locus before beingallowed to solidify, thereby avoiding damage to the fibers. This optionis the subject of a co-pending U.S. patent application, now U.S. Pat.No. 4,112,203.

The present invention is not limited to the specific cells of FIGS. 1-4,which are for purposes of illustration, and is limited only according tothe following claims.

What is claimed is:
 1. A process for fabricating an essentiallystress-free battery cell comprising a closed casing having two externalelectrical terminals and an inner assembly disposed within said casingand electrically connected to said terminals,said process comprisingsteps I, II and III as defined below, step I being carried out and thenone of steps II and III, followed by the other; I. providing, as saidassembly, an assembly which includes (1) a plurality of hollow fibersadapted to function as the electrolyte/separator in a battery cell and(2) an element incorporated in and extending from said assembly andengaged with said casing to provide the sole support and positioning ofthe assembly within the casing so that the assembly does not otherwisecontact the casing in a manner which imposes a potentially damagingstress on any part of the assembly or which will result in suchstressing if thermally induced dimensional changes occur in theassembly; II. so engaging said element with said casing, and III.forming a separate, electrical connection from each of said terminals tosaid assembly, at least one of the connections comprising a limp linkand each terminal connected to said assembly by a limp link not beingconnected by any non-limp member to said assembly.
 2. The process ofclaim 1 wherein:said element is a protruding portion of a tank definedby a tubesheet and an upper member which has the general configurationof an inverted cup or funnel and is sealingly engaged at its bottom edgewith the peripheral portion of the tubesheet, and step II is carried outby engaging said tank portion with a wall of the casing adjacentthereto.
 3. The process of claim 2 in which said upper member comprisesan upward extending, generally tubular section, the casing top walldefines an opening, and step II comprises positioning the assembly andcasing top so that said tubular section extends through said opening andforming a generally annular, rigid seal between the outer surface of thelatter section and the surrounding portion of the casing top wall. 4.The process of claim 2 in which:the peripheral portion of said tubesheetprotrudes from said assembly as a ridge, said casing is provided as two,separated, generally cup-shaped sections, each having a flared andradiused rim and being provided with an electric conductor extendingthrough the cup bottom in sealing engagement therewith, the protrudingportions of said conductors constituting said external terminals, stepIII is carried out by:(a) connecting to the inner portion of each ofsaid conductors an end of a separate, limp, electrically conductive foilstrip, (b) inverting one of said casing sections and connecting the freeend of the foil strip joined therewith to said assembly, (c) connectingthe free end of the foil strip joined with the other casing section tosaid assembly, and, step II is carried out by bringing together saidcasing sections around said assembly, while folding the two foil strips,in such manner that the casing rims are disposed in flush contact witheach other and together form a bulge defining a groove, in the innersurface of the casing wall, in which the protruding portion of thetubesheet is disposed, and then sealingly engaging said rims with eachother.